Reelgood providing bad data
The data coming from Reelgood on what is available where is incorrect. For example:
https://trakt.tv/search/movies/?watchnow=netflix&genres=fantasy,science-fiction&years=1880-1989
That query (Sci-Fi/Fantasy on Netflix released before 1990) gives 8 results - but two of them (*Batteries Not Included and The Neverending Story) are not available on Netflix.
Similar issues with Amazon Prime showing results that are simply not available.
I checked over at Reelgood, and the problem is clearly on their end as they're displaying the same wrong results. But it does render this feature of trakt pretty useless. Can anything be done from your end?

Closing since this is ultimately a fix from Reelgood and Trakt will auto update as they improve their links.
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Maxwelldeux commented
Thanks for looking into it! It all seemed fine until a few days after Christmas.
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AdminJustin (Founder, Trakt) commented
Not much can be done on our end unfortunately. I have been in contact with Reelgood and they indicated they are working to improve their link quality and working to make this more accurate. Once they start implementing that, Trakt should automatically start improving as well.